Three dimensional, continuous and configuration heat soldering

ABSTRACT

A system for continuously and configurationally heat soldering layered sheets of plastic, concomitantly with embossing a distinctive pattern across at least one face of the heat soldered seam. The disclosed system has at least one pressing face that includes the mirror image of the pattern to be embossed across a face of the seam, engraved therein. Pressing faces embedding electrical heaters provide for embossing a changeable content across the faces of the seam. Sealing band a pattern engraved across a face of which provides according to the present invention for embossing distinct three-dimensional geometrical shapes across the faces of the heat-soldered seams. A seam that is heat soldered according to the present invention continuously extends across two-dimensional contours of significant widths. Three-dimensional features having distinct sectional shapes protrude off the seam at least towards one direction.

FIELD OF THE INVENTION

The present invention relates in general to imprinting graphical features across a surface of plastic. In more particular the present invention relates to continuously and configurationally heat soldering three dimensional features, across surfaces of layered sheets of plastic and to sealing packaging made of plastic.

BACKGROUND OF THE INVENTION

A system and method for imprinting a pattern along a seam that is heat soldered across layered sheets of plastic is disclosed in international patent application the publication number of which is WO10055516 A1. Selected contours across the surface of the layered sheets of plastic are first heated to a predefined temperature that is close and lower compared to the melting point of the plastic considered. Soldering heads of the disclosed system comprise a molding member having a plurality of pressing faces. These pressing faces provide for forcing the layered sheets of plastic towards each other as well as towards a supporting surface or a mold that presses against them from the opposite side of the layered sheets of plastic. The footprints of these pressing faces are disposed within the heated contours. These footprints have distinctive graphical shapes of specific graphical and/or typographical features. The heated contours across the layered plastic cool off by conducting excessive heat towards the molding member, the supporting surface, or the mold onto which the layered plastic is compressed. Cooling by transferring heat to the ambient atmosphere is accomplished as well. Seams that are heat soldered according to the disclosed method are normally fragmented into a plurality of different and spaced apart segments within each of which the layered sheets of plastic are mutually soldered to each other. Such segments include a distinctive feature or features of the pattern imprinted along the seam considered. The disclosed soldering heads and the disclosed method provide for stepwise and/or intermittent soldering process.

Three dimensional seams are typically heat soldered for structurally strengthening seams that seal off plastic bags such as bags that are used for storing beans, or pouches for storing fluids. The plastic sheets that are utilized for manufacturing such bags and/or pouches are normally made of laminated plastic foils. The melting point of the inner layer of such laminated foils is relatively low. Therefore these inner layers are fused when are suitably heated and further are adhered to the inner layer of a neighboring laminated plastic sheet when are suitably compressed. However the melting temperature of their external layer is relatively high. Such that the external plastic layer will nit melt when it engages the heated surfaces of the soldering device. Therefore the external layer can sustain temperatures which are normally significantly higher compared to the melting point of inner plastic layers. As a result the layered plastic can be suitably structured and receive a desired three dimensional profile while being compressed by means of the heated surfaces of the soldering device. The internal plastic layers fuse and mutually adhered to each other while are such compressed. Whereas the external layers are not distorted when are cooled down after such pressing while heating is accomplished. Therefore a three dimensional profile of a seam which is undistorted is such produced.

Commercially available heat-seal jaw bar assemblies normally provide for heat sealing plastic bags. Such heat-seal jaw bar assemblies has an integral sealing band and a housing that provides for gripping together the edges of layered sheets of plastic, and compressing them towards the sealing band. Heat seal jaw bar assembly that is especially suited for security applications, such as used by banks for packing money during storage and transport and/or by Police Forces around the UK for “tamper-proof” protection of drugs' evidence, or property carrying finger prints, and the like, are commercially available. Exemplary is the product named HM 900 S Security Coding Machine provided by Hulme Martin Heat Sealers Ltd., Woking, England, that provides a user for embossing a text and/or graphical content within the contours of the heat soldered seam. One of the jaws of this device is a gravure in which the mirror image of the content to be embossed across the seam is engraved. The other jaw is a common heat seal. However the width of the heat seal of this device is significantly larger compared to the width of the gravure. Therefore the heated region across the surface of the layered plastic sheets is wider compared to the width of the pattern. As a result spacing is generated between the edge of the embossed pattern and the edge of the heat soldered seam. Such spacing provides an unauthorized user for cutting open at the margin of the seam of such manufactured bags and reseal them back in a way that is hard to recognize by an authorized user. Endless heat sealing bands that are normally made of stainless steel coated with polytetrafluoroethylene (PTFE) known as Teflon® are common in the marketplace and are normally employed for continuously heat soldering layered sheets of plastic. Such bands can be incorporated in heat sealing devices having an integral motor or linked to a motor that rotates the sealing band across a face of the layered sheets of plastic. Seams of desired widths and lengths can be heat soldered by means of such heat-seal jaw bar assembly and/or endless sealing bands incorporated in soldering devices as further described infra.

A system for continuously and configurationally heat soldering layered sheets of plastic providing for: i. producing seams that continuously extend across a surface of the layered sheets of plastic within contours having any desired widths and lengths; ii. producing seams having distinctive patterns embossed across both opposing faces of a seam; iii. producing seams in which the edges of the embossed pattern overlap the edges of the soldered seam margins of which are relatively narrow; iv. increasing the quality and distinctiveness of the imprinted patterns; v. increasing the rates of soldering as well as the associated production rates, such system is beneficial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B are two isometric views of two pairs of pressing faces each of which describes a device for continuously and configurationally heat soldering three dimensional patterns across layered sheets of plastic according to two different embodiment of the present invention respectively;

FIGS. 1C-1D are a sectional view and an isometric view of a pair of pressing faces of a device for continuously and configurationally heat soldering three dimensional patterns across layered sheets of plastic according to another embodiment of the present invention;

FIG. 2 is a scheme of a device for continuously and configurationally heat soldering three dimensional patterns across layered sheets of plastic according to another embodiment of the present invention;

FIG. 3 is an isometric view of a pair of pressing faces of a device for imprinting three dimensional and changeable patterns across layered sheets of plastic;

FIG. 4A is an isometric view of a segment of a device for continuously and configurationally heat soldering layered sheets of plastic according to a preferred embodiment of the present invention;

FIG. 4B is an isometric view of a segment of a device for continuously and configurationally heat soldering layered sheets of plastic according to another preferred embodiment of the present invention;

FIG. 5 is an isometric view of a device for continuous and configurationally heat soldering according to an embodiment of the present invention;

FIG. 6A is an isometric view of a soldering head of a sealing station according to an embodiment of the present invention;

FIG. 6B is a sectional view along line AA shown in FIG. 6A.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In accordance with the present invention a system for continuously and configurationally heat soldering layered sheets of plastic is provided. The present invention concerns heat soldering a seam along which at least two separate sheets of plastic are mutually attached to each other, or at least one sheet of plastic is securely attached to a piece of plastic bar or a flange such as a flange enclosing aperture of a container for sealing off this aperture.

The term continuously heat soldering means according to the present invention that heat soldered seams, which are normally elongated, have a substantial width of a significant dimension. Namely, seams of the invention continuously extend across two dimensional contours. The width of a seam according to the present invention is of at least a number of millimeters (mm). The geometrical shapes of the edges of seams that are heat soldered according to the present invention are linearly flat, curvilinear, wavy and/or zigzagged (such as saw tooth) and/or any combination thereof. Edges of pressing faces which are not flat linear are referred hereinafter as wavy edges. However, edges of the embossed pattern closely overlap the respective edges of the soldered seam, such that spacing that are positioned nearby edges of seams of the invention, which may separate between the edge of the pattern embossed therein and the edge of the seam are narrower compared to one mm.

Additionally or alternatively, the term continuously means that the soldering process is not necessarily intermittent but continuously on going. Namely the process of heat soldering seams across layered plastic is carried out while the layered plastic considered is continuously progressed through a device, system, station and/or apparatus for heat soldering layered plastic. Additionally or alternatively the term continuously means according to the present invention that the pattern imprinted along a seam, which are heat soldered across the layered sheets considered, is changeable on-line. Namely the pattern considered changes at least from one segment of a heat soldered seam to the successive soldered segment of the same seam.

The term configurationally heat soldering means according to the present invention that a distinctive pattern is imprinted along the seam concomitantly with its being heat soldered. Such imprinted pattern according to the present invention can be visualized, or at least felt by touching across each face of the two opposing faces of the heat soldered seam. The features of this pattern include three dimensional features the cross section of which are of distinctive geometrical shapes such as: lines which are dashed, dotted, broken, curvilinear, wavy or wiggly; closed and two dimensional geometrical contours such as circles, ellipse, star, or polygonal; graphical symbols, graphical features, typographical features and alphanumerical characters.

The term layered plastic refers according to the present invention to two or more separated sheets, or foils of plastic that are layered one across the other. Alternatively, the layers are arranged by folding one sheet of plastic into, say two segments, which are layered one across the other; or a cylindrical sleeve the opposing sides of which are flattened such that circumferential circles (of the cylindrical sleeve) transform by such flattening into a linear segment. Alternatively a foil such as a cover a segment of which is layered across a piece or flange of solid plastic, such as the edge of an aperture of a container or a tray made of plastic.

The layered plastic considered herein below have at least one and more often two planar faces each of which is disposed at the respective side of the two opposing sides of the heat soldered seam considered.

The term plastic refers hereinafter to sheets, pieces or segments of bars or flanges such as those that are typically structured at the rim of apertures of plastic containers, all of which are made of thermoplastic resins such as: high and/or low density polyethylene (HDPE, LDPE), as well as coextruded low/low, low/high and high/high density polyethylene (LLDPE, LHDPE, HHDPE); polypropylene, polystyrene, polyesters, polyethylene terephthalate (PET) and/or co-extruded sheets including any combination of the above mentioned materials, and/or sheets of plastic foam, bubbled sheets, and/or sheets made of nonwoven fabric such as Tyvek®, which is made of high density polyethylene fibers; Complex sheets of plastic that include foils of different plastic resins such as the co-extruded sheets described above are considered hereinafter as different sheets that are layered one across the other. Layered sheets of plastic in which at least one of the sheets is made of non woven fabrics such as Taft or Rayon that engages a sheet made of any of the aforementioned thermoplastic resins are also considered according to the present invention as layered sheets of plastic. However, only cases in which the melting temperature of at least one of the external layers of the layered plastic sheets is relatively close to the melting temperature of any of the internal layers are considered layered plastic according to the present invention. Namely cases in which the melting temperature of at least one external layer closely equal, or is close up to say a few degrees centigrade to the lowest melting point of any of the layered sheets of plastic are in accordance with the present invention. Whereas cases in which the melting point of an external layer is significantly higher compared to the melting temperature of an adjacent inner layer are not considered layered plastic according to the present invention

Configurationally heat soldering according to the present invention may also provide for structurally strengthening connection along the heat soldered seam, as known. Exemplary are three dimensional structures that are typically embossed along seams that seal off apertures of pouches their sidewalls are made of laminated plastic foils containing a metallic layer and/or paper such as pouches normally employed for containing sauces or spices. Configurationally heat soldering according to the invention may additionally serve a manufacturer for personalizing such sealed packaging of by imprinting logo and/or trademark along the seam. Such personalizing is relevant in cases in which authenticity of a product or the expiration time associated with the product is considered. Plastic bags and especially tamper evident plastic bags that are sealed off by means of configurationally heat soldering according to the present invention are characterized by the distinctive pattern that is present along the seams. Any unauthorized opening of the sealed package and resealing it back involves corrupting the distinctive features of such pattern. Therefore a user may easily recognize when breaching of the sealed package has occurred.

Reference is first made to FIGS. 1A-1B in which isometric views of segments of two pairs of pressing faces that respectively belong to two devices for continuously and configurationally heat soldering according to two different embodiments of the present invention are respectively shown. In FIG. 1 pair 10 of pressing faces is shown. The layered sheets of plastic are to be sandwiched and compressed between these pressing faces for being mutually heat soldered. Bulges 12 protrude off pressing face 14. The height of each of these bulges measured relative to pressing face 14 is lower compared to at most half of the accumulative thickness of the layered plastic to be sandwiched between these pressing faces. Cases, in which the height of bulges 12 is lower compared to the thickness of the outermost sheet of the layered sheets of plastic, while this sheet is not externally stressed, are in accordance of the present invention. Normally such height is of a few hundreds of micrometers. Each of these bulges points towards pressing face 16. These bulges are shaped as alphabetic characters engraved across pressing face 14 which is the face of band 18 that faces band 20. Band 18, as well as pressing face 14 and bulges 12 are made of hard material, such as stainless steel coated with Teflon®. Such coating provides for decreasing the risk that fused plastic will stick to bulges 12 and/or pressing face 14. Cases in which the body of a pressing face is made of a composite material having good thermal conductivity and a surface coated with silicon are in accordance of the present invention. The faces of the bulges as well as the background formed by the segments of pressing face 14 that are located adjacent to the bulges, collectively form a mirror image of the pattern or patterns to be embossed across the targeted surfaces. A common heat-sealing band across one face of which the mirror image of a distinctive pattern is engraved implements band 18. Such engraving can be accomplished by laser cutting, milling, machining, adhering, mold pressing, coating and/or chemically etching. The body of band 20 is typically made of stainless steel. The face of band 20 facing band 18 is covered with vulcanized silicon. Both pressing faces are forced against opposing surfaces of the layered sheets of plastic. When the layered sheets of plastic are compressed between both pressing faces band 18 is electrically powered to produce electric pulsed heating along a predefined time interval. Such heated pressing face 14 conducts excessive heat towards the surface of the layered sheets of plastic across the entire area which is engaged with pressing face 14. This area includes the segments of the background across which bulges 12 of pressing face 14 are disposed. The level of the electric voltage, the pulse widths in time and the number of pulses to be fed to band 18 along the aforementioned predefined time interval are selected in consideration with the ohmic resistance and heat capacity of band 18, as well as the heat capacity of the sandwiched sheets of plastic. Such selected working parameters ensure that at least one layer of the layered sheets of plastic will reach a desired and predefined temperature. The layered sheets of plastic are further compressed between the pressing faces along a second predefined time interval after the pulsed heating is stopped. Namely this second time interval provides for cooling the layered sheets of plastic. At the end of the second time interval the heat soldering process of the seam considered is accomplished. The continuous pressure exerted unto the layered plastic during the heating and the cooling minimizes the level by which the plastic shrinks and provides for avoiding the risk of distorting the embossed pattern and/or generating wrinkles along the seam. The geometrical shape of a seam such heat soldered fits in with the projection of pressing face 14 across the surface of the layered sheets of plastic. Namely, a distinctive pattern identical to the mirror image of the faces of bulges 12 is embossed across this surface of the layered sheets of plastic. Recesses their depths comply with the height of bulges 12 (which is typically of 1-2 tenths of millimeter) are formed across the face of the seam at the footprints of the respective bulges. Respective bulges can be recognized across the opposite face of the seam at least by touching. Therefore such accomplished continuous and configurationally heat soldering provides for embossing three dimensional patterns along the seam.

In FIG. 1B pair 28 of pressing faces 30 and 32 is shown. Pressing face 30 coincides with a face of band 34, whereas pressing face 32 is the face of band 36 that faces band 34. Bulges shaped as alphabetic characters protrude off pressing face 30. The height of the bulges 37 measured relative to the plane of pressing face 30 is lower compared to the accumulative thicknesses of the layered sheets of plastic. Recesses 38 that fit in with the respective bulges are structured across pressing face 32. In cases in which the edges of the pressing faces considered are fiat, a caution must be taken considering the widths of the margin of the embossed pattern according to the present invention. The widths of the spacing designated by pairs of arrows 41 which correspond to the widths of spacing separating between an edge of the female pattern and a respective edge of band 36 (and similarly between an edge of respective bulges and the corresponding edges of band 34, not shown) which fit in with respective edges of the heat soldered seam, are relatively small and do not exceed a number of tenths of a millimeter. Both bands 34 and 36 can be implemented by common heat-sealing bands that are typically made of stainless steel coated with Teflon®. Engraving the respective faces of these heat seal bands is accomplished by means of laser cutting, machining, milling, carving and/or etching, as known. For heat soldering layered sheets of plastic both pressing faces 30 and 32 are first forced against the respective surfaces of the layered sheets of plastic. The compressed sheets are squeezed by both pressing faces. However segments of the layered sheets that face respective bulges are stretched and fill in the spacing separating between the surfaces of each of the bulges and the surfaces of respective recess. Any of both bands can be according to the invention heated to a predefined temperature. Heating the layered sheets can be effected by conduction when the band considered is pressed against a heating block having the same desired and predefined temperature. Alternatively heating can be electrically effected similarly to the pulsed heating technique described hereinabove. Heating is carried out along a first predefined time interval. By the end of this first time interval the heating is stopped and the sandwiched layered sheets of plastic cool off along a second and predefined time interval. By the end of such cooling the heat soldering process is accomplished. The seam such produced has a geometrical shape that overlaps the geometrical shape of the formerly heated pressing face. However the pattern embossed along the seam when is visualized across the side of the layered plastic that faces band 32 fully comply with the pattern formed by the bulges of pressing face 30. Similarly the pattern visualized across the opposite side of the layered sheets overlaps the pattern structured by the recesses disposed across pressing face 32. Therefore the embossed pattern across both faces of the seam includes three dimensional features. Any bulge that is structured across one face of the seam is associated with a respective recess disposed at the opposite face of the seam.

Pressing faces carrying a pattern to be embossed by heat soldering across one face of the layered plastic having bulges protruding off their surface are referred hereinafter as male pressing faces. Pressing faces carrying a pattern to be embossed by heat soldering across one face of the layered plastic having recesses sagging across them are referred hereinafter as female pressing faces. Embodiment variants in which the pressing face carrying a pattern to be embossed by heat soldering across one face of the layered plastic, which are made of relatively hard material such as metal are in accordance with the present invention. A pair of pressing faces of a device of the invention may have a female pressing face made of a hard material, whereas the other pressing face is a male pressing face made of a relatively soft material. The bulges protruding off this face need not exactly fit in with the recesses of the female pressing face. However in cases in which the desired pattern to be embossed along the seam is three dimensional at least portions of the faces of the bulges of the male pressing face have to overlap portions of the apertures of respective recesses of the female pressing face as further described infra. A pair of pressing faces which is in accordance with another embodiment of the present invention has a male pressing face made of metal whereas the other pressing face is planar or cylindrical that is also rotatable. The last two pressing faces are made of soft material such as vulcanized silicon rubber. Any of the pairs of pressing faces described above provides for producing three dimensional patterns along a soldered seam similarly to the pair described with reference to FIG. 1A hereinabove.

Reference is now made to FIGS. 1C-1D. In FIG. 1C a sectional view of a pair of female pressing faces of a device for continuously and configurationally heat soldering according to another embodiment of the present invention is shown. Pair 42 of two female pressing faces each of which is disposed across the respective face of band 43. Both bands 43 are made of metal, such as Teflon® coated stainless steel. Recesses 44, are structured across both pressing faces of pair 42. The cross section of each of recesses 44 has a distinctive geometrical shape. The depth of any of the recesses 44 is significantly lower compared to the accumulated thickness of the unstressed layered sheets of plastic divided by two. The spatial distribution, or the geometrical shapes, of the recesses of one pressing face need not fit in with the geometrical shapes or positions of the respective recess of the other pressing face across the first face. Namely, the patterns that respectively comply with the mirror image of any of these pressing faces need not overlap.

For continuously and configurationally heat soldering these layered sheets of plastic by employing this pair 42, first the layered sheets of plastic are sandwiched between both pressing faces of pair 42. Then electric pulsed heating of both pressing faces is accomplished by feeding a series of electric pulses of predefined width in time, repetition rate and electrical power along a first predefined time interval to both bands 43. The heated plastic fuses and is further driven by the pressure exerted by the pressing faces into the volumes enclosed within the respective recesses. The heating is immediately followed by cooling the sandwiched sheets of plastic along a second predefined time interval. Cooling is accomplished by radiating and conducting heat to the ambient atmosphere. Alternatively cooling is accomplished by conducting the excessive heat to a cooling block through which coolant is driven, as described infra. The seams such heat soldered are characterized with a series of bulges that protrude off both faces of the seam that are respectively positioned across both opposing sides of the layered sheets of plastic. When visualized the face of the seam includes a soldered region having a significant width which is continuous, and serves as a background from which bulges of plastic protrude. The geometrical shape of each of these bulges complies with the geometrical shape of the respective recess sagging into the respective pressing face. The geometrical shape of the background region complies with the contours of the spacing that are present across the respective pressing face at the peripheries of the recesses. In FIG. 1D an isometric view of a segment of pair 42 shown in FIG. 1C is shown. The wavy edges of both pressing faces, are preferable according to the present invention, provides for enhancing the immunity of the heat soldered seam against breaching. These wavy edges make it more difficult to cut open any of the layers that are such mutually attached and reseal them back again such that a user will not recognize that the sealing has been breached.

A device for continuously and configurationally heat soldering layered sheets of plastic according to an embodiment of the present invention is hereby described with reference to FIG. 2 to which reference is now made. Each pressing face of a pair of pressing faces 51 is respectively attached to base block 52 and top block 53. Base block 52 is secured to frame 54, whereas top block 53 is movably attached to frame 54. Top block 53 is movable between two positions. One of these positions is an open position in which top block 53 is positioned way above base block 52. Top block is moveable all the way down to the point in which band 56 presses against band 58 by a predefined force. Or alternatively until the distance separating between a pair of outermost points, each of which disposed at a respective pressing face of pair 51, reaches a threshold of minimal distance. For moving top block 53 from the open position to the compressing position shaft 60 is rotated about its axis in the direction shown by curved arrow 62. For changing the position to an open position shaft 60 is rotated in the opposite direction. Biasing springs, not shown, provide for tuning the level of force to be exerted by both pressing faces onto the sandwiched sheets of plastic at the compressing position. Alternatively a tunable angular lock, not shown, provides for limiting the angle by which shaft 60 can be rotated in the direction shown by curved arrow 62, such that the distance between a pair of the outermost points located at any of both pressing faces will not get lower than a minimal predefined distance. Heat-seal band made of stainless steel coated with Teflon® implements band 56. The side edges of band 56 are preferably wavy, not shown. In cases in which these edges are flat, the widths of the spacing separating between edges of the pattern engraved onto band 56 and the respective edges of band 56 do not exceed according to the present invention a few tenths of millimeter. The face of band 56 that faces band 58 onto which a distinctive pattern is engraved implements the male pressing face of pair 51. The upper face of band 58 is made of vulcanized silicon and as such implements the other pressing face of pair 51. Suitable electronic circuitry and a system controller that are housed in a close by cabinet, not shown, provides for generating series of electric pulses that powers band 56 to produce electric pulsed heating. Piping embedded within base block, not shown, provide for delivering coolant for cooling band 58 in cases in which relatively high rates of soldering are desired. Device such as described above is similar to common heat-seal jaw bar assembly that is normally employed for manually sealing plastic bags. Such device as described hereinabove can be conveniently used for manually and continuously and configurationally heat soldering. The respective edge of the layered sheets of plastic is introduced in between the pressing faces when the top block is in the open position. Such introduction is accomplished from the side opposing the side in which frame 54 is positioned. At this stage shaft 62 is rotated all the way in the direction of curved arrow 62. When the device gets into the compressing position the top block is automatically locked at the compressing position relative to frame 54. The operator presses a dedicated operating switch installed at a gripping handle disposed at the free end of shaft 60. Series of electrical pulses is activated according to the working parameters stored in the system memory. Suitable working parameters, such as the number of pulses, their time width and voltage, the length of the first and second time intervals, as well as the level of force to be exerted by each pressing face onto each surface of the layered sheets of plastic can be experimentally derived in advance as further described infra. Selected working parameters are loaded by the operator into the memory of the system controller at the initiation of the heat soldering process. The device automatically stops heating the layered sheets of plastic by the end of the stored value of the first time interval. The device remains at the compressing position, namely the top block remains locked all along the second time interval. By the end of the second time interval the sy

ts the operator for moving the top block to the open position and releasing the currently soldered sheets of plastic off the device.

A similar device can be incorporated as a soldering station into an automatic production line for producing, and/or sealing filled, plastic bags. Optionally the manually rotated shaft that provides for moving the top block is replaced with a hydraulic or electric press that is linked to the system controller. Thereby changing from an open position into a pressing position can be automatically accomplished. Additionally a system of rotating cylinders and suitable stretching mechanisms is introduced. Such system provides for propagating the layered sheets of plastic towards the soldering station and further pulling the soldered sheets away. Each of the sheets considered is winded off a dedicated role around which virgin sheets of plastic are originally stored. The system of the rotating cylinders and stretching mechanisms is such arranged that the various sheets are continuously and synchronously layered one across the other while are propagating towards the soldering station, as known. Tuning the level of force to be exerted by a pressing face onto the layered sheets of plastic in cases in which the system considered (either an automatic soldering station or the manual device that was described above) has a hydraulic press. The operator starts the soldering process at a relatively low pressure level. Then the operator gradually raises this level up to the point in which the quality of the three dimensional features as well as the entire soldered seam is satisfactory. In systems having biasing springs the operator may tune the level of force by modifying the distance that the top block moves down to the compressing position. The operator may control the magnitude of this distance by employing a gearbox that provides for stepwise process in which this distance is modified by a few hundredths of millimeter per a full rotation of a tuning screw. Automatic soldering stations such as described above can have gearbox that provide for tuning this distance in steps of a few micrometers. Nevertheless, the operator starts soldering at a relatively large separating distance and gradually decreases its magnitude down to the point in which the quality of the seam is satisfactory. The above mentioned predefined temperature of the layered sheets of plastic according to the present invention is close to, and below, the melting point of the layer of plastic considered. At this temperature this layer fuses such that the adjacent layer or layers stick to this layer when the various layers are forced towards each other. The inventor of this patent application has experimentally found that: regions disposed at different location across the surface of the layered sheets of plastic, although heated by the same heating power, along the same time interval, however were not forced towards each other failed to be mutually adhered, compared to regions in which respective compressing was applied in addition to the heating along the same time interval. For producing a soldered seam of an acceptable quality according to the present invention the compressed sheets have to be cooled following the step in which heating and pressing are concomitantly effected. Therefore such compressing continues after heating is stopped along the second time interval. The levels by which the layered sheets of plastic are heated and further cooled off are similarly experimentally set. The operator gradually modify the level of heating power to be conducted towards the layered sheets of plastic as well as the respective length of the first and second predefined time intervals until he finds the suitable levels for which the quality of the soldered seam is satisfactory. Embodiment variants of the soldering device described above having any combination of pressing faces as described with reference to FIGS. 1A-1D are in accordance with the present invention.

Reference is now made to FIG. 3 in which a pair of pressing faces of a device for configurationally heat soldering three dimensional patterns according to another preferred embodiment of the present invention is shown. The features of the distinctive pattern embossed along the soldered seam by means of this device can be modified on-line. Namely the pattern that is currently heat soldered changes on-line such that the pattern to be embossed along the seam that successively follows the current soldered seam is different compared to the pattern that is currently embossed. Pressing face 70 of pair 72 is tiled with thick film heaters, such as tile 73. Thick film heaters are commercially available, such as those provided by Watlow® of St. Louis, Mo., USA. The heaters are typically housed within a package that is made of ceramic and stainless steel. Therefore pressing face 70 is the relative hard surface onto which the layered sheets of plastic have to be pressed. Each of the tiles has a two dimensional array of circular heating elements, such as elements 74. All the heating elements of pressing face 70 have common ground. However each element is independently connected to the other pole of a power supply having the same common ground. By electrically powering various circular heating elements of an array, selected geometrical shapes as well as alphanumerical characters can be imprinted across the surface of layered sheets of plastic that are sandwiched and compressed between pressing faces 70 and 76. Pressing face 76 is the combined surface which is formed by the union of the circular faces of the cylindrical bulges 78 that protrude off band 80 and point towards pressing face 70. Band 80 is made of stainless steel; the cylindrical bulges are made of vulcanized silicon rubber. Such pair of pressing faces can be installed in a device and/or an automatic soldering station as described herein above with reference to FIG. 2. Seams heat soldered by means of such device may include changeable content such as the date and/or a serial number of each package.

For soldering a seam having a distinct pattern of three dimensional features of an acceptable quality by means of the aforementioned manual system or the automatic soldering station, each of which has the pair of pressing faces described with reference to FIG. 3; the following steps has to be carried out:

-   -   i. the layered sheets of plastic have to be introduced and         further sandwiched between these pressing faces;     -   ii. the layered sheets have to be compressed at a predefined         pressure level;     -   iii. the layered sheets have to be selectively heated to a         predefined temperature along a predefined first time interval,         wherein only selected heating elements are electrically powered         each time, and wherein heating concomitantly effected with the         pressing, and     -   iv. the layered sheets have to be further immediately cooled off         while the layered sheets are still being compressed along a         second predefined time interval.

The spacing separating between any pair of adjacent heating elements prevents the production of a geometrically continuous seam across the layered sheets of plastic. However when the male pressing face is forced against the layered sheets of plastic at the suitable force level recesses are structured across one surface of the layered sheets whereas bulges can be at least felt by touching across the surface disposed at the opposite side. In a case in which the area of the circular heating elements does not exceed a first predefined limit and the spacing separating between adjacent heating elements does not exceed a second predefined limit layered sheets of Tyvek® can be heat soldered by means of such manual device and/or automatic soldering station described hereinabove. Tyvek is a non woven fabric made of fibers of polyethylene that are heated and further compressed. Both the first as well as the second aforementioned limits can be experimentally found, as sheets of Tyvek® of a significant number of styles change their color, becomes transparent and brittle and tend to be easily crumpled when are first heated up to temperature that is close to, and lower compared, to the melting point of polyethylene. This feature stands as long as the area of the heated region across the surface of a sheet of Tyvek® exceeds a maximal threshold. Therefore when the spacing between adjacent regions that are exposed to such heating and further cooling does not exceed the first and second aforementioned limits, the color of the sheet within the area considered does not change and the sheet continue to have its mechanical features as a virgin Tyvek®.

Reference is now made to FIG. 4A, in which an isometric view of a segment of device 90 for continuously and configurationally heat soldering layered sheets of plastic according to a preferred embodiment of the present invention is shown. Endless band 92, which is made of rubber, constitutes one pressing face of the device considered. Sprocket wheel 93 and 93′ provide for continuously and cyclically rotating band 92 in the direction shown by arrows 94. Endless and rotatable heat-seal band 96 is closely disposed below the lower segment of endless band 92. Spacing of predefined height separates between the highest points disposed along band 96 and the external face of band 92. Bulges having distinctive and three dimensional geometrical shapes protrude off the external face of band 96, not shown. As such the external face of band 96 constitutes the male pressing face of the pair of both pressing faces (which are the external faces of bands 92 and 96). Pulleys 98 and 98′ provide for continuously and cyclically rotating band 96 in the direction shown by arrows 99. The external face of both bands 92 and 96 which constitutes the respective pressing faces, is the face opposing the respective inner face that engages sprockets 93, 93′ or pulleys 96, 96′ respectively. Heating block 100 is such disposed below the inner face of the upper segment of band 96 such that it is slidingly attached to band 96. Similarly cooling block 102 that is adjacent to heating block 100 is slidingly attached to the inner face of band 96. Optionally internal piping leading coolant, not shown, is structured within the body of cooling block 102. Pressing block 104, which is positioned above the inner face of the lower segment of band 92 provides for forcing both pressing faces one towards the other at a predefined level of force. At the initial stage of a session of heat soldering pressing block 104 is positioned at an open position in which the dimension of spacing 97 provides for introducing the layered sheets of plastic in between both pressing faces. The level of temperature of the heating block is automatically regulated by means of an electric heater that is placed within cavity 105 and a suitable electrical circuit, not shown. The operator introduces the free end of the layered sheets of plastic in between both pressing faces such that it enters spacing 97. Then the operator moves pressing block 104 from the open position into the compressing position in which the compressed sheets are forced by both pressing faces at the above mentioned predefined force level. From this moment on layered sheets of plastic such sandwiched and compressed, are progressed through device 90 by means of both rotating bands 92 and 96. Heat is conducted towards the sandwiched sheets of plastic along a first time interval along which the segment of layered plastic considered faces heating block 100, such that the temperature of at least one sheet of plastic reaches the predefined temperature. Heat is conducted off the sandwiched sheets along a second time interval along which they are progressed along the full length of the cooling block. Therefore a segment of the seam having the mirror image of the pattern that is present along the respective segment of the male pressing face is soldered across the surface of the layered sheets of plastic. This segment of the seam is been just soldered along the segment of the layered sheets that just passed across both heating and cooling blocks. The operator is able to set the level of the desired and predefined temperature of the heating block, which is close, and below, the melting point of the plastic resin considered, by means of a system controller, not shown. The above mentioned electrical circuit provides for retaining the temperature of the heating block at the desired and predefined temperature that is stored in the memory of the system controller. For given lengths, of the heating block which is designated by 106, as well as of the cooling block, that is designated by 108, a suitable level of the translational speed of both pressing faces, across the heating and cooling blocks is selected by the operator. Selecting the translational speed is experimentally achieved in consideration with the aforementioned predefined temperatures and the lengths of the first and second time intervals. The operator according to the present invention experimentally selects the respective levels of the working parameters of system 90. Some of these parameters include the predefined force level, predefined temperature, the first and second time intervals and the translational speed. The process for setting working parameters for system 90 is similarly to the experimental process described above considering setting working parameters for the manual system and/or the soldering station. Namely, in such experiments the operator fixes the level of all parameters except one of them which he or she gradually changes the level of this working parameters, say the translational speed, or the pressing force, and examines the quality of the respective soldered seam and the distinctive pattern imprinted along it. Such trials related to a tunable working parameter continue until the point in time in which the quality of the respective soldered seam is satisfactory. System 90 fairly provides for heat soldering any kind of plastic sheets described herein above. Care has to be taken when heat soldering sheets made of Tyvek® by employing this system. Namely, the dimensions of the bulges of the male pressing face as well as the spacing separating between any adjacent bulges have to comply with the maximal limits of the respective dimensions as described hereinabove.

Alternatively, in accordance with another preferred embodiment of the present invention, endless band 92 is substituted with a metallic band; thereby the pair of pressing faces of the system considered is similar to the pair described with reference to FIGS. 1A-1D. Seams produced by such system consist of a union of separated contours within each of which at least two of the layered sheets are mutually heat soldered to each other. These contours have a distinctive three dimensional shape which form a mirror image of the pattern engraved along the respective pressing faces. For example, a system similar to system 90 which is in accordance with another preferred embodiment of the present invention has a different pair of pressing faces. One of the pressing faces is identical to the male pressing face that is implemented by endless band 96. A metallic band substitutes endless band 92. Recesses disposed along its face form a pattern that is identical with the mirror image of the pattern structured along band 96. Both bands are synchronized such that bulges of band 96 fit into respective recesses when they engage them. Namely, the pair of pressing faces of this device complies with the pair of pressing faces described with reference to FIG. 1B hereinabove. Furthermore, in accordance with another preferred embodiment of the present invention, the pair of pressing faces of a system similar to system 90 includes a female pressing face having a distinctive pattern formed by a plurality of recesses; the other pressing face of this pair is a male pressing face such as the male pressing face described with reference to FIG. 3 hereinabove. The seams soldered by means of any of the last three described systems are characterized by an embossed pattern that is three dimensional. However, the patterns produced by the device having male and female pressing faces, each of which is made of a relatively hard material are of better quality. These seams have two dimensional soldered contours that extend across ranges of significant lengths and widths of a considerable magnitude. Such seams include the features of the embossed patterns that are surrounded with a background of soldered seam. However the side edges of at least one pressing face are preferably according to the present invention wavy. Alternatively the widths of the spacing separating between edges of the patterns and respective edges of the pressing faces has according to the present invention to be lower compared to a few tenths of millimeter. The seams produced by means of a device the pressing faces of which include a pressing face that is made of a relatively soft material are characterized by a union of separated contours. Each of such contours overlaps a segment of the layered sheets of plastic in which at least two of these sheets are mutually heat soldered. Additionally, in cases in which two endless bands both having male pressing faces or both having female pressing faces such as described with reference to FIGS. 1C-1D, respectively substitute endless bands 92 and 96, the seams such produced are characterized with series of bulges or recesses that are disposed on both opposing faces of the layered sheets of plastic. In FIG. 4B an isometric view of a segment of a device 130 for continuously and configurationally heat soldering layered plastic according to another preferred embodiment of the present invention is shown. Endless male sealing band 132 has a wavy edge for embossing a wavy seam across the layered plastic to be heat soldered by means of this heat soldering device.

Reference is now made to FIG. 5 in which an isometric view of device 180 for continuously and configurationally heat soldering layered sheets of plastic is shown. Layered sheets of plastic 182 are pulled by the rotating drums 183 and 184, such that they encircle drum 184 and gets off its cylindrical enclosure after they complete encircling drum 185. Soldering head 188 provides for heat soldering laterally relative to the axis of layered sheets 182. Piston 190 provides for forcing soldering head 188 towards the layered plastic along a first time interval, along which the layered plastic is first heated to a predefined temperature. Then pressing continues along a second time interval along which the sandwiched plastic cools off such that the currently heat soldered seam is hardened. Meanwhile such pressed soldering head 188 rotates synchronously with drum 184 in the direction shown by curved arrow 186. By the end of both the first and second time intervals piston 190 draws back the soldering head which is rotated in the opposite direction shown by curved arrow 192 to the place in which it waits for the successive lateral seam to be heat soldered across the continuously progressing layered sheets 182. Axially imprinting across layered sheets 182 is accomplished by means of endless sealing band that is schematically shown by curved line 196. Such endless sealing bands are rotated by drums 194 while are being forced towards the circumference of drum 184. Inside the space that separates between both drums 194 a heating block and a respective cooling block are such mounted that along their respective faces the back of the endless sealing bands are slidingly moved while the endless sealing band is rotated around these drums 194.

EXAMPLE 1

Following are two exemplary cases in which configurationally heat soldering is required such that the imprinted content is changeable on line. A manufacturer of a product which is associated with an expiration time may desire to also emboss his trademark across the seams of the packaging thereby indicating the authenticity of the packaged product. Alternatively a remote branch of a bank packs currency notes within sealed temper evident envelopes prior to transporting them to the main office. Heat soldering for sealing the packaging of the product as well as sealing of the temper evident envelopes can be accomplished by employing the manual device described with reference to FIG. 2. However the pressing faces considered has to provide for embossing changeable content such as by using the pressing faces described with reference to FIG. 3. The system controller of the device for configurationally heat soldering is such programmed that all the information and graphical features that are fixed and do not change from one product unit or temper evident envelope to the other, are such allocated that a predefined portion of the electric heaters of the respective pressing face are successively powered during each time a seam is heat soldered. Such that the same content will be repeatedly embossed along seams that successively seals each and every package or envelope. A field of suitable number of digits, say ten digits is allocated to the expiration date in the first example. Optionally additional field is allocated to a serial number and a catalog number of the product considered. In the case in which currency notes are considered one field is allocated to the total sum of the money contained in each and every envelope whereas another is allocated to the serial number of the envelope.

EXAMPLE 2

Food products, such as dairy products, are normally packaged in sealed packaging for decreasing a risk of microbiological contamination. Common sealing covers which are made of laminated plastic foils are heat soldered to the sidewalls of say, cup packs, to seal off the content thereby safeguarding the hygienic conditions of the content therein. Quite often the only reason for utilizing laminated plastic foils as sealing covers is the need to attach such covers to the respective containers' sidewalls by means of heat soldering. The exterior surface of the laminated foil which is often metalized can sustain the high temperatures such as those experienced when common sealing dies are employed. Such temperatures exceed by far the melting point of the inner layer of the laminated foil, which is normally made of polyethylene. In a case in which the polyethylene layer would have been exposed to the temperature of the sealing die the layer would have been completely melted and could not have been heat soldered to the sidewall of the container considered by means of common sealing dies. The temperature gradient that is generated across the width of the laminated foil provides for moderating the temperature experienced by the polyethylene layer down to the point in which the layer fuses such that it sticks to the adjacent layer of plastic. However, a significant cost saving can be achieved by substituting the laminated plastic foils with a foil such as any of the following foils which are significantly less expensive: high and/or low density polyethylene (HDPE, LDPE), as well as co-extruded low/low, low/high and high/high density polyethylene.

For this purpose the sealing dies currently employed have to be substituted with soldering heads of the present invention. The respective working temperatures of a soldering head of the present invention can be tuned to be at a close proximity to, and lower than, the melting temperature of the rim of the aperture of a plastic receptacle that is considered. Reference is now made to FIGS. 6A-6B. In FIG. 6A soldering head 200 of an exemplary sealing station of a production line for packaging of, say yogurt, within cup packs, according to an embodiment of the present invention is shown. Soldering head 200 is positioned above cup pack 201 the sealing of which by means of cover 202 has been just accomplished. Cover 202 is a segment of foil made of a thermoplastic material such as polyethylene.

For sealing off cup pack 201, first cover 202 is positioned above the aperture of cup 201 to cover it. The pressing face of soldering head 200 (which is the face of soldering head 200, which faces cup pack 201) is forced at this stage against the rim of cover 202 at a predefined force level. The rim of cover 202 overlaps the flange that surrounds the aperture of cup 201. Normally the sidewalls of the cup pack can sustain the pressure exerted by the pressing face of sealing die 200. However a sealing station having a second pressing face, which provides for pressing against the sidewall of cup 201 towards the opposite direction in which the first pressing face presses, is in accordance with the present invention. soldering head 200 is concomitantly heated by means of electrical pulsed heating, as known, while its pressing face forces the cover along a first predefined time interval. Heating is such accomplished that the pressed segment of the layered plastic that includes the full width of the cover and a portion of the flange that surrounds the aperture of cup 201, reaches a predefined temperature. This predefined temperature is close and lower compared, to the melting point of the cover. At this stage pressing the rim of the cover against the flange that surrounds the aperture of cup 201 is continued, at the same level of force, along a second predefined time interval. Along the second time interval the heated segments of plastic cool off. Cooling is accomplished by transferring the excessive heat to the ambient atmosphere. By the end of the second predefined time interval cover 202 is heat soldered to sidewall 203 of cup pack 201. Optionally the connection between cover 202 and the sidewall of the cup is strengthened by means of a structural strengthening as further described below. Arcuate bulge 206 the cross section of which is shaped as a triangle provides for curving a segment of cover 202 towards, and forcing the curved polyethylene foil into, the body of sidewall 203. The sidewalls of groove 208 serve as structural strengthening that is introduced into the connection between cover 202 and sidewall 203. Quite often such structural strengthening is required for example to avoid leakage of oil off the package by capillarity. In cases in which the content of the sealed package comprises oil, such as in a case in which the content of the receptacle to be sealed off is a sesame paste (tahini) the sealing is implemented by two or more successively arranged closed grooves, such as groove 208, that completely surround the aperture of the container. However when dry content or water based content is considered a simple flat seam is sufficient for completely sealing the packaging. Therefore a sealing die that provides for sealing off a receptacle which is made of thermoplastic resin by means of a cover made of a foil of such as polyethylene according to an embodiment of the present invention, such sealing die includes a flat ring made of a sealing band, such as ring 212. The minimal width of ring 212 provides for fusing a portion of the cover such that a continuous seam that seals off the aperture of cup 201 is generated when this portion cools off. In cases in which additional strengthening structures are required, flat ring 212 which is made of a segment of sealing band, or cut from a sheet of stainless steel coated with Teflon® or silicon, and one or more arcuate bulges arranged in close loops are disposed across its pressing face.

Alphanumeric characters 210 engraved on the pressing face of sealing die 200 provide for embossing a text along the seam that seals off the aperture of cup 201, as well as for additional structural strengthening. In FIG. 6B a cross sectional view along line AA of a detail shown in FIG. 1 is shown. 

1. A tamper evident packaging made of layered sheets of plastic, wherein at least one of said layers which is the first sheet of plastic heat soldered to at least one item along a seam a portion of which positioned across a surface of said first sheet of plastic, and wherein said item selected from a group of items consisting of another sheet of plastic which is the second sheet of plastic and is different from said first sheet, a piece of bar made of plastic, a segment of a flange made of plastic, and any combination thereof, said tamper evident packaging comprising a seam at least a segment of which continuously extends across a two dimensional contour, two sides of which overlap the edges of said segment of seam respectively each, and wherein the geometrical shape of at least one of said edges selected from a group of geometrical shapes consisting of linearly flat, curvilinear, wavy, zigzagged and any combination thereof, and wherein a pattern embossed within said two dimensional contour, and wherein said pattern comprises at least one feature having a distinctive three dimensional geometrical shape, and wherein the melting temperature of said first sheet of plastic is relatively close up, to a number of degrees centigrade, to the melting temperature of said at least one item.
 2. A tamper evident packaging as in claim 1, wherein said pattern has at least one edge, and wherein the distance between said at least one edge and said at least one edge of said seam does not exceed one millimeter.
 3. A tamper evident packaging as in claim 1, wherein said pattern is changeable.
 4. A tamper evident packaging as in claim 1, wherein said pattern comprises at least two bulges each of which respectively protrudes towards opposing directions.
 5. A tamper evident packaging as in claim 1, wherein said pattern comprises at least two recesses each of which has an aperture, and wherein each of said apertures respectively facing opposing directions.
 6. A tamper evident packaging as in claim 1, wherein said layered sheets of plastic comprises sheets of plastic selected from a group of sheets of plastic consisting of sheets of plastic foam, bubbled sheets, sheets made of a nonwoven fabric, selected from a group of nonwoven fabrics consisting of heat compressed high density polyethylene (Tyvek®), Taft and Rayon, and any combination thereof.
 7. A device for continuously and configurationally heat soldering layered sheets of plastic, said device comprising at least one pressing face which is the first pressing face, wherein said first pressing face has two edges, which are spaced apart by at least a number of millimeters, and wherein the geometrical shape of at least one of said two edges selected from a group of geometrical shapes consisting of linearly flat, curvilinear, wavy, zigzagged and any combination thereof, said first pressing face is operative in forcing at a predefined force level against a surface of said layered sheets of plastic, wherein said forcing accomplished while heating said layered sheets of plastic along a first predefined time interval, and wherein said first pressing face is further operative in forcing while cooling said layered sheets of plastic along a second predefined time interval, and wherein said at least one pressing face comprises a member selected from a group of members consisting of a pattern engraved on a segment of a sealing band, a plurality of electric heating elements and any c

nd wherein said pattern comprises at least one feature having a distinct three dimensional geometrical shape.
 8. A device as in claim 7, further comprising another pressing face which is the second pressing face and is different from said first pressing face, and wherein said second pressing face comprises a pattern engraved on a segment of a sealing band, and wherein each of said first and second pressing faces is a male pressing face.
 9. A device as in claim 7, further comprising another pressing face which is the second pressing face and is different from said first pressing face, and wherein said second pressing face comprises a pattern engraved on a segment of a sealing band, and wherein each of said first and second pressing faces is a female pressing face.
 10. A device as in claim 7, further comprising another pressing face which is the second pressing face and is different from said first pressing face, and wherein said second pressing face comprises a pattern engraved on a segment of a sealing band, and wherein one of said first and second pressing faces is a female pressing face, and wherein the other of said first and second pressing faces is a male pressing face.
 11. A device as in claim 7, wherein said heating effected by electrical pulsed heating.
 12. A device as in claim 7, further comprising a heating block, and wherein said first pressing face slidingly movable along said heating block at a given translational velocity along a first predefined time interval.
 13. A device as in claim 12, further comprising a cooling block, and wherein said first pressing face slidingly movable along said cooling block at said translational velocity along a second predefined time interval.
 14. A device as in claim 7, further comprising a frame and a sealing band, which is an endless sealing band that is moveable relative to said frame.
 15. A heat soldering head for sealing off aperture of receptacles the rim of which comprises a thermoplastic resin, by means of plastic foils, said soldering head comprising at least one pressing face for forcing at a predefined force level along a first predefined time interval against a surface of said plastic foil, wherein said forcing concomitantly effected with heating a segment of said plastic foil to a predefined temperature which is close to the melting point of said plastic foil and is lower compared to the melting point of said plastic foil, and wherein said at least one pressing face comprises a member selected from a group of members consisting of a segment of a fiat sealing band, a segment of a sealing band across which a pattern is engraved, a plurality of electric heating elements and any combination thereof, and wherein the melting temperature of said plastic foil is relatively close to the melting point of said thermoplastic resin up to a number of degrees centigrade.
 16. A soldering head such as in claim 15, wherein said at least one pressing face is operative in forcing against said surface of said plastic foil along a second predefined time interval after said heating is accomplished. 